Various known prosthetic devices assist the user in walking by simulating the movement and forces on a human ankle applied by the Achilles tendon and calf muscle as a person walks. In certain cases, a counter-torque is applied to the ankle joint during certain phases of the walking cycle to assist the user. Often the amount of torque is determined by a model or calculation and applied by a motor controlled by the model. To determine the amount of counter-torque that should be applied by the motor, it is necessary to determine the amount of torque that is being applied by the user to flex the ankle joint during normal walking.